The use of elongated surgical cutting instruments has become well accepted in performing dosed surgery such as arthroscopic or, more generally, endoscopic surgery. In dosed surgery, access to the surgical site is gained via one or more portals, and instruments used in the surgical procedure must be elongated to permit the distal ends of the instruments to reach the surgical site. Surgical cutting instruments for use in closed surgery—also known as “shavers”—have an elongated outer tubular member terminating at a distal end having an opening in the end or side wall (or both) to form a cutting window and an elongated inner tubular member concentrically disposed in the outer tubular member and having a distal end disposed adjacent the opening in the distal end of the outer tubular member. The distal end of the inner tubular member has a surface or edge for engaging tissue via the opening in the outer tubular member and cooperates with the opening to shear, cut or trim tissue. The inner tubular member is rotatably driven about its axis from its proximal end by a handpiece having a small electric motor which is controlled by finger actuated switches on the handpiece, a foot switch or switches on a console supplying power to the handpiece. The distal end of the inner tubular member cart have various configurations depending upon the surgical procedure to be performed, and the opening in the distal end of the outer tubular member has a configuration to cooperate with the particular configuration of the distal end of the inner tubular member. These various configurations are referred to generically as shaver blades. Cut tissue is aspirated through the hollow lumen of the inner tubular member to be collected via a vacuum tube communicating with the handpiece.
Resection of tissue by a shaver blade is accomplished by cooperative interaction between the edges of the inner and outer cutting windows. As the inner and outer windows come into alignment, the tissue is sucked into the lumen of the inner tube with a vacuum. Continued rotation of the inner member causes the inner cutting edges to approach the outer cutting edges. Tissue in the cutting window between the inner and outer edges is either trapped between the edges or ejected from the window. Tissue trapped between the edges is either cut by the edges as they approach each other or torn by the cutting edges as they pass and rotate away from each other. The resected tissue is aspirated from the site through the inner lumen of the inner tube.
Angled shaver blades, which are shaver blades having an outer tube in which a distal portion is angularly offset from a proximal portion, increase the ease with which a surgeon is able to access certain tissues and locations within the surgical field. Curved shavers are well known in the art, such as shown in U.S. Pat. No. 5,437,630 to Daniel et al, U.S. Pat. No. 5,411,514 to Fucci et al, and U.S. Pat. No. 5,961,532 to Finley et al. In general, angled shavers have an outer tubular member with a linear proximal portion and a linear distal portion joined by a curved portion such that the distal portion is angularly offset from the proximal portion. The rotatable inner member is an assembly which has a rigid linear proximal portion, and a rigid linear distal portion having a distal end configured for cutting or abrading tissue. A flexible portion couples the distal end of the proximal linear portion and the proximal end of the linear distal portion together.
Angled shavers may be divided into two categories according to the construction of the flexible portion of the rotatable inner member. The first category includes shavers having flexible portions formed of couplings made of metallic materials. Such couplings are made of one or more layers of helically formed sheet or springs. The coupling may be formed from multi-layer couplings having the helixes or coils of adjacent layers formed in opposite directions, i.e. a right-hand helix adjacent to a left-hand helix, so as to increase the torsional strength of the coupler. Such construction is disclosed by U.S. Pat. No. 5,411,514 to Fucci et al., U.S. Pat. No. 6,533,749 to Mitusina et al., and by others.
The second category includes angled shavers in which the flexible portion of the rotating inner member is made of a polymeric material. Such construction is disclosed by U.S. Pat. No. 5,961,532 to Finley et al., U.S. Pat. No. 5,540,708 to Fucci et al., U.S. Pat. No. 5,922,003 to Anctil et al., U.S. Pat. No. 6,620,180 to Bays et al. and others. The simplified construction of a shaver with polymeric flexible portions results in decreased manufacturing costs.
During use, tissue occasionally lodges in the lumen of the distal portion of the Inner tubular member. These “clogs” prevent effective use of the instrument and must be removed by the surgeon so that the operation can continue. To remove a clog, the instrument is withdrawn from the joint. The inner tubular member is removed from the outer member and a wire or other declogging device inserted into the distal end of the inner member to dislodge the tissue obstructing the lumen. It is essential that a shaver blade be constructed in a manner which allows the inner drive assembly to be easily removed from the outer housing. In the case of angled shavers, removal of the inner drive assembly is complicated because the straight distal portion of the inner drive assembly must pass through the curved portion of the outer tube. Because of this complication, the diameter of the distal linear portion of the inner drive assembly is less than the diameter of the lumen of the curved portion of the outer tube to facilitate easy withdrawal. However, even with this configuration, significant proximal axial force must be applied to the proximal end of the inner drive assembly to withdraw the inner drive assembly from the outer housing. The withdrawal resistance is generally greater for inner assemblies with polymeric flexible portions, especially those having flexible portions made from homogeneous high-strength polymers such as PEEK (polyetheretherketone). The rigidity of these polymeric materials creates high frictional forces between the flexible portion of the inner drive assembly and the curved portion of the outer housing. The rigidity of these materials also creates high frictional forces between the rigid distal portion of the inner drive assembly and the curved portion of the outer tube, and between the rigid distal portion of the inner drive assembly, and the linear distal portion of the outer housing during the initial portion of withdrawal. The axial forces on the rigid distal portion of the inner drive assembly may dislodge the inner drive assembly from the distal end of the flexible portion. The forces also tend to cause failure of the assembly at the juncture between the distal end of the proximal rigid portion of the inner drive assembly and the proximal end of the flexible portion. In view of these potential failures, the attachment of the polymeric portion to the rigid portions of the inner drive assembly must be capable of transmitting torsional forces to effect the cutting or abrading of tissue and preventing failure of the inner drive assembly during disassembly.
There exist various methods of attachment. For instance, U.S. Pat. No. 5,540,708 to Lim et al. discloses use of laterally opposed protrusions on the proximal end of the inner drive and mating grooves in the distal end of the flexible portion of the inner drive assembly to transmit torque to the drive. Barbs are included on the proximal end of the protrusions penetrate the side walls of the slots in the polymeric portion so as to retain the drive on the polymeric portion when the drive is subjected to axial tensile forces. This method of attachment is expensive because machining is required to create the slots in the polymeric material and corresponding protrusions on the inner drive. Also, the strength of the joint when subjected to axial forces is relatively weak because the drive is retained to the polymeric portion only by four small barb portions which embed themselves in the slot walls of the polymeric portion. Because of manufacturing tolerances and the resulting variations in component features sizes, the amount of penetration of the barb portions into the walls of the polymeric tube slots will vary significantly with resulting variation in the retention strength.
U.S. Pat. No. 5,922,003 to Anctil et al. discloses an inner drive having a proximal portion with a reduced diameter having various holes or elongated slots of various configurations. The slots extend between the inner and outer cylindrical surfaces of the reduced portion. The proximal portion of the drive, which is slightly larger in diameter than the lumen of the tubular portion, is assembled into the distal end of the polymeric tubular portion. The joint is heated to a temperature at which the polymeric material in the overlapping region flows into the holes and passages of the drive proximal region so as to form a mechanical bond having torsional and tensile strength. The device taught by Anctil et al. uses a polymeric material having a low melting point and relatively low strength and rigidity. The necessary strength and rigidity are achieved through a wire mesh that is embedded in the polymeric portion. This bonding method cannot be used with higher rigidity, higher strength materials such as PEEK.
U.S. Pat. No. 5,961,532 to Finley et al. discloses a method of attachment in which a tubular flexible transition shaft has a lumen of varying diameters. Specifically, the lumen has regions of increased diameter at its proximal and distal ends to form “annular flanges”. The proximal portion of the inner drive and the distal portion of the proximal rigid portion of the inner drive assembly have reduced diameters and are textured with “hills and valleys”. The distal and proximal portions of the lumen of the flexible transition shaft with larger diameters have “complementary hills 65 that seat in the valleys of annular flange 62”. The mechanical interlocking of the complementary features enables the joints to transmit torque and provides tensile strength. However, the process of forming the complementary features on the inner lumen portions and annular flanges is problematic because the walls of the tubular segments are quite thin and forming such features causes the walls to deform.
Thus, there is a need for an improved connection for joining a polymeric flexible portion of a shaver blade inner drive assembly to a rigid distal tip and to the flexible transmission shaft of the assembly. In addition, there is a need for an improved connection that is easy to produce and provides high torsional and axial strength when used with high-strength polymeric materials, such as PEEK.